This invention relates generally to bearing assemblies and, more particularly, to bearing assembly materials.
Gas turbine engines generally include a high pressure compressor, a combustor, and a high pressure turbine. Compressed air flows through the engine while fuel is mixed with the compressed air and ignited to form a high energy gas steam in the high pressure compressor and combustor, respectively. The high pressure compressor, combustor, and high pressure turbine are sometimes collectively referred to as a core engine. Such gas turbine engines also may include a low pressure compressor for supplying compressed air, for further compression, to the high pressure compressor, and a fan for supplying air to the low pressure compressor.
The high pressure compressor typically includes a rotor surrounded by a casing. The casing is typically fabricated to be removable, such as by forming the casing into two halves that are then removably joined together. The high pressure compressor includes a plurality of stages and each stage includes a row of rotor blades and a row of stator vanes. The casing supports the stator vanes, and the rotor supports the rotor blades. The stator vane rows are between the rotor blade rows and direct air flow toward a downstream rotor blade row.
Variable stator vane assemblies are utilized to control the amount of air flowing through the compressor to optimize performance of the compressor. Each variable stator vane assembly includes a variable stator vane which extends between adjacent rotor blades. The variable stator vane is rotatable about an axis. The orientation of the variable stator vane affects air flow through the compressor.
A known variable vane assembly includes a variable vane, a trunnion seal, and a washer. The variable vane assembly is bolted onto a high pressure compressor stator casing and the trunnion seal and washer surround an opening that extends through the casing. The variable vane includes a vane stem that extends through the opening in casing and through the trunnion seal and washer. The seal and washer are referred to herein as a bearing assembly. The bearing assembly produces a low friction surface that prevents metal on metal contact. Such variable vane assemblies have possible air leakage pathways through the openings in the casing. Also, the high velocity and high temperature air causes oxidation and erosion of the bearing assemblies, which may lead to failure of fibers within the bearing assembly, and eventual failure of the variable vane assembly.
Once the bearing assembly fails, an increase in leakage through the opening occurs, which results in a performance loss. In addition, failure of the bearing assembly allows contact between the stator vane and the casing, which causes wear and increases overhaul costs of the engine.
Accordingly, it would be desirable to provide bearing assemblies fabricated from materials having performance characteristics that will reduce or eliminate air leakage between the stator vane stem and the compressor casing. In addition, it would be desirable to provide an increase in the durability of the seal and washer composition to increase part life.